- A short synthesis of (S)-2-(diphenylmethyl) pyrrolidine, a chiral solvating agent for NMR analysis
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A three step synthesis of (S)-2(diphenylmethyl)pyrrolidine 4 is described which allows its preparation on a large scale. The C2 symmetric diamines 5 and 6 have been prepared from 4 and are attractive as potential ligands for asymmetric transformations. Pyrrolidine 4 has been assessed as a chiral solvating agent for the NMR analysis of chiral compounds. It emerges as a good CSA for carboxylic acids and some secondary alcohols.
- Bailey, David J.,O'Hagan, David,Tavasli, Mustafa
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- Basicities and Nucleophilicities of Pyrrolidines and Imidazolidinones Used as Organocatalysts
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The Br?nsted basicities pKaH (i.e., pKa of the conjugate acids) of 32 pyrrolidines and imidazolidinones, commonly used in organocatalytic reactions, have been determined photometrically in acetonitrile solution using CH acids as indicators. Most investigated pyrrolidines have basicities in the range 16 aH aH aH 12.6) and the 2-imidazoliummethyl-substituted pyrrolidine A21 (pKaH 11.1) are outside the typical range for pyrrolidines with basicities comparable to those of imidazolidinones. Kinetics of the reactions of these 32 organocatalysts with benzhydrylium ions (Ar2CH+) and structurally related quinone methides, common reference electrophiles for quantifying nucleophilic reactivities, have been measured photometrically. Most reactions followed second-order kinetics, first order in amine and first order in electrophile. More complex kinetics were observed for the reactions of imidazolidinones and several pyrrolidines carrying bulky 2-substituents, due to reversibility of the initial attack of the amines at the electrophiles followed by rate-determining deprotonation of the intermediate ammonium ions. In the presence of 2,4,6-collidine or 2,6-di-tert-butyl-4-methyl-pyridine, the deprotonation of the initial adducts became faster, which allowed the rate of the attack of the amines at the electrophiles to be determined. The resulting second-order rate constants k2 followed the correlation log?k2(20 °C) = sN(N + E), where electrophiles are characterized by one parameter (E) and nucleophiles are characterized by the two solvent-dependent parameters N and sN. In this way, the organocatalysts A1-A32 were integrated in our comprehensive nucleophilicity scale, which compares n-, -, and σ-nucleophiles. The nucleophilic reactivities of the title compounds correlate only poorly with their Br?nsted basicities.
- An, Feng,Maji, Biplab,Min, Elizabeth,Ofial, Armin R.,Mayr, Herbert
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supporting information
p. 1526 - 1547
(2020/02/04)
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- Organocatalytic enantioselective synthesis of nitrogen-substituted dihydropyran-2-ones, a key synthetic intermediate of 1β-methylcarbapenems
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Organocatalytic enantioselective cycloadditions providing nitrogen-substituted dihydropyran-2-ones were developed in two catalytic systems. The (3R,4R)-product was a versatile intermediate in the synthesis of 1β-methylcarbapenem antibiotics.
- Kobayashi, Shoji,Kinoshita, Tatsuhiro,Uehara, Hisatoshi,Sudo, Tomoko,Ryu, Llhyong
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supporting information; experimental part
p. 3934 - 3937
(2009/12/05)
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- Stereoselective Synthesis of Trifluoromethylated Compounds: Nucleophilic Addition of Formaldehyde N,N-Dialkylhydrazones to Trifluoromethyl Ketones
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The nucleophilic 1,2-addition of formaldehyde N,N-dialkylhydrazones 1, 2, and 7-10 to trifluoromethyl ketones 3a-e takes place in the absence of any catalyst or promoter to afford a series of α-hydroxy-α-trifluoromethylhydrazones (4, 5, and 11-14) in good-to-excellent yields. From the several reagents studied, optimal results were achieved using 1-(methyleneamino)pyrrolidine (2) for the synthesis of racemic adducts and (S)-l-(methyleneamino)-2-[1-(methoxy)diphenyl-methyl]-pyrrolidine (10) for the asymmetric version of the reaction. The resolving properties of the chiral auxiliary carried by 10 allowed an easy Chromatographic (flash) separation of any obtained diastereomeric mixture. Thus, a single operation rendered moderate-to-good amounts (42-75%) of optically pure adducts (S,S)-14 (de > 98%) by combining excellent chemical (82-92%) and moderate optical (51-81%) yields. Hydrazones 5 and (S,S)-14 were protected by benzylation [→ 16 and (SJS)-18] and then transformed into benzyl-protected α-trifluoromethyl cyanohydrins 21 by MMPP oxidative cleavage and into α-benzyloxy-a-trifluoromethyl aldehydes 22 by ozonolysis. Alternatively, adducts 5 and (S,S)-14 were methylated [→ 19 and (S,S)-20] and transformed into the corresponding α-methoxy-α-trifluoromethyl carboxylic acids 24 by successive ozonolysis and in situ oxidation (NaClO2, tBuOH, isobutene) of the crude a-methoxyaldehydes.
- Pareja, Carmen,Martin-Zamora, Eloisa,Fernandez, Rosario,Lassaletta, Jose M.
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p. 8846 - 8854
(2007/10/03)
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- LARGE SCALE PREPARATION OF VERSATILE CHIRAL AUXILIARIES DERIVED FROM (S)-PROLINE
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The synthesis of a variety of enantiomerically pure chiral auxiliaries based on (S)-proline and bearing sterically demanding side chains at the pyrrolidine moiety, such as the secondary amines (S)-3,5 and 7 and the hydrazines (S)-6, is described on a molar scale.As key step, the Grignard or RLi addition to the N-benzylated proline ester (S)-1 is used.
- Enders, Dieter,Kipphardt, Helmut,Gerdes, Peter,Brena-Valle, Leonardo J.,Bhushan, Vidya
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p. 691 - 704
(2007/10/02)
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